Presently, the art of retreading tires involves various methods and apparatus. Perhaps the most historically employed method is a "cold-capping" or "pre-cure retreading" operation which includes the following steps:
1. Remove the old, worn, or damaged tread.
2. Buff the tire carcass to provide a moderately textured surface for the adhesion of new tread rubber.
3. Apply a suitable adhesive to the textured carcass surface.
4. Apply a thin layer of a cold, calendered sheet of uncured cushion gum material to the circumferential periphery, or crown surface, of the tire carcass.
5. Apply a pre-cured tread band over the cushion gum.
6. Cure the cushion gum to bond the tread rubber integrally to the tire carcass.
To use the above-described "cold-capping" method, the cushion gum material was historically pre-manufactured in the form of a calendered sheet. The sheet is slit to various standardized widths and coiled with a plastic release film interposed between successive wraps of the sheet. The prepared coils of cushion gum would be maintained in inventory in a wide variety of widths until a need arises for cushion gum of that particular width.
Various problems are inherent to the above-described practice, and they include the need for rigorous inventory control to assure availability of the correct width and thickness of cushion gum for each tire carcass that might be encountered. The result is often at odds with the need for a timely turnover of the material in order to avoid deleterious aging of the stock on the shelf. In addition to aging, the stored coils of cushion gum are also subject to contamination, particularly along the exposed edges of the coiled cushion gum. The coils are also subject to oxidation as well as physical damage during handling.
As noted, this procedure requires that the crown surface on the tire carcass be buffed and then treated with an adhesive, or cement compound, prior to the application of the cold cushion gum. The adhesive may be applied by painting with a brush or by a roller or by spraying. Any of these processes require the expenditure of time and materials resulting in an increase in the retreading cost. Following the application of the adhesive, the operator selects the proper strip of cushion gum to be applied. The operator may have to search among the available inventory to locate a strip of the correct length, width and thickness. One end of the strip is manually applied to the carcass by the operator. The operator then operates a spin control to cause the tire carcass to rotate while a tensile force is being applied to the strip as it is maintained in alignment with the circumference of the carcass. When the entire circumference of the tire carcass is covered, the operator will stop the rotation of the carcass, retro-rotate the carcass slightly and cut the strip to length. The ends of the strip are then spliced in an overlapped fashion. The strip of cushion is stitched to the tire casing and the protective release film is removed. Thereafter the precured tread stock is manually applied and hand spliced (edge to edge). This splice is generally secured with staples.
One proposed solution to the problems found in the present practice of using calendered rolls of cushion gum stock is to limit the number of widths of the pre-manufactured gum stock maintained in inventory and trim the edges of the cushion gum after it has been applied to the tire carcass. Such an approach requires that wider-than-necessary rolls of cushion gum be customized to fit the width of several sizes of tire carcasses. Obviously, this proposal suffers not only from being wasteful but also from being labor-intensive.
In any event, the historic method of cold-capping with pre-calendered cushion gum requires that the user manually position the leading edge of a single, wide, strip of cushion gum fully across tile crown of the tire carcass and then rotate tile carcass through one revolution to wind the cushion gum about the circumference of the tire carcass with the release film facing radially outwardly. The presence of tile release film tends to preclude contamination of the radially outer surface of the cushion gum, which would occur without the release film if tile worker were not careful. The release film also permits the gum to be coiled without the successive layers adhering to each other and allows external stitching.
It should also be understood that faulty placement of the leading edge (generally mis-alignment) often requires that the initial portion of the cushion gum sheet be peeled off the tire carcass and be restarted. Of course, this tedious procedure may result in damage to tile cushion gum sheet and/or degradation to the adhesion required between the cushion gum sheet and the crown surface of the tire carcass.
Typically, tile entire circumferential extent of the tire carcass was wrapped with the cushion gum sheet prior to "cutting-in" the required splice. The cushion gum ply would then be roller-stitched to the tire carcass and the release film stripped off in preparation for the application of the pre-cured tread.
To alleviate some waste encountered with the above-described "cold-capping" practice, coiled rolls of calendered cushion gum material having an overall length sufficient to provide a stated plurality of tire carcasses of a given circumferential dimension are maintained in inventory. These rolls, while of a specific length for ease of handling, are not usually of an exact length to cover a specific number of tire carcasses, even if the rolls are intended to be for use with an exceedingly common tire size. Thus, short lengths of calendered gum material are generally discarded as excess, thus comprising waste stock. This practice obviously results in an additional cost to the operation.
Another historic method and apparatus available in the industry for retreading tires is known as the "hot-capping" procedure. The hot-capping procedure, and an exemplary apparatus for performing that method, are described in U.S. Pat. No.--U.S. Pat. No. 3,251,722 and U.S. Pat. No. 3,177,918--to R. G. Holman. According to the "hot-capping" technique, uncured tire tread material is layered onto the crown, and perhaps a portion of each shoulder, of a tire carcass to a sufficient radial thickness that the tire carcass, with the tread material adhering to the circumference thereof, can be received within a mold to form the tread design and to cure the tread rubber in situ.
The above-described "cold-capping" and "hot-capping" methods are distinctly different by reason of the type and condition of tire tread stock applied to the tire carcass and they are, therefore, considered non-related, or disassociated, technologies by knowledgeable entities working in this art.
More recently, the retreading industry adopted a method which extrudes, a hot cushion gum compound in a continuous spiral across at least the crown of a tire carcass in order to prepare the carcass for receiving a pre-cured tread stock. This is perhaps the most advanced method yet known, and while it works exceptionally well, and has greatly obviated the negative aspects of the prior art methods and apparatus, the present invention is deemed to be a still further improvement over the application of the hot cushion gum in a spiral path.